Subnetid

Subnet ID, short for subnet identifier, is the portion of an IP address that identifies a subnetwork within a larger network. It is defined by the subnet mask in IPv4 or by the prefix length in IPv6. The Subnet ID represents the network address of the subnet and is used by routers to determine which subnet a packet should be routed to. In many contexts it is also called the network address.

In IPv4, the Subnet ID is obtained by performing a bitwise AND between the IP address and the subnet mask. For example, the address 192.168.10.7 with a subnet mask of 255.255.255.0 has a Subnet ID of 192.168.10.0. The full subnet range runs from the network address (the Subnet ID) up to the broadcast address (the Subnet ID with all host bits set to one). When written in CIDR notation, this subnet is 192.168.10.0/24, where the /24 indicates the length of the Subnet ID.

In IPv6, the Subnet ID serves a similar role but within a different addressing scheme. Subnets are created by varying the bits after the network prefix, and the remaining bits identify the specific subnet and the interface on a device. A common practice is to use a 64-bit network prefix with subnets identified by the next bits, though the exact size of the Subnet ID depends on the deployment’s prefix allocation.

Overall, the Subnet ID is the portion of an IP address that designates the specific subnetwork, enabling efficient routing and address organization within larger networks.